VATICAN CITY (Reuters) - Pope Francis attended but did not preside at an Easter vigil service in St. Peter's Basilica on Saturday night, presumably because of recurring leg pain that has forced him to curtail some activities.

       Italian Cardinal Giovanni Battista Re replaced the pope as the main celebrant at the service, which involved a procession in near-total darkness up the central nave of Christendom's largest church.

       The pope sat at the front of the basilica in a large white chair on the side and appeared to be alert. The Vatican said he would read the homily later in the Mass.

       The 85-year-old pope suffers from sciatica, which causes pain in one leg and results in a pronounced limp. Recently Francis also has had a flare up of pain in his right knee.

       The condition appears to come and go.

       He had to curtail some of his movements during a trip to Malta at the start of April but on Friday afternoon, he was well enough to walk the entire aisle both at the start and the end of a Good Friday service in the basilica.

       (Reporting by Philip Pullella)